Preparation of additives for electroplating baths



United States Patent 3,515,653 PREPARATION OF ADDITIVES FOR ELECTROPLATIN G BATHS Ronald Sykes, Selby, England, assignor to The Yorkshire Dyeware & Chemical Co. Ltd., Selby, England No Drawing. Filed Dec. 8, 1966, Ser. No. 600,062 Int. Cl. C23b /14 US. Cl. 204-54 6 Claims ABSTRACT OF THE DISCLOSURE The invention provides new additives for electroplating baths particularly for deposition of tin which are either a reaction product of a sulphonating agent and certain aromatic hydroxy compounds or a condensation product of such a reaction product with formaldehyde. The additive is conveniently stored and used as an aqueous concentrate.

The present invention relates to organic additives for electroplating baths, particularly those used for the elec trodeposition of tin.

In the continuous electroplating of tin on strip iron or steel in an acid type bath, small quantities of organic addition agents such as dihydroxy diphenyl sulphone have been used to obtain bright even deposition of the tin over as wide a range of current density conditions as possible. Without such additives the tin deposited is dull and the range of current density conditions is much narrower.

It is an object of the present invention to provide new additives for acid-type electroplating baths used in the electroplating of tin on iron or steel.

According to the present invention there is provided a reaction product of a sulphonating agent and at least one aromatic hydroxy compound having the general formula:

wherein:

R and R are each selected from the group consisting of hydrogen and alkyl groups having from 1 to 4 carbon atoms,

R and R are each selected from the group consisting of hydrogen, an alkyl group having from 1 to 4 carbon atoms and the hydroxyl radical, and in which one of the R radicals and one of the R radicals is a hydroxyl radical,

R is hydrogen when one R is an alkyl radical and is selected from the group consisting of hydrogen and an alkyl group having from 1 to 4 carbon atoms when one R radical is hydrogen,

R is hydrogen when one R is an alkyl radical and is selected from the group consisting of hydrogen and an alkyl radical having from 1 to 4 carbon atoms when one of the R radicals is hydrogen.

Preferably the aromatic hydroxy compound is one in which in the general formula the radicals R to R do not represent in total more than two alkyl groups. Preferably the alkyl groups are methyl groups. The most preferred of the aromatic hydroxy compounds is di-(p-hydroxyphenyl)-dimethyl-methane.

The reaction products of the present invention are useful as additives for electroplating baths for the electrodeposition of tin on strip iron or steel. Such additives ice may comprise the reaction product itself or they may comprise condensation products of the reaction product with formaldehyde or with a substance releasing formaldehyde. In a further embodiment therefore, the invention provides an additive for an electroplating bath which comprises a reaction product as defined above, or a condensation product thereof with formaldehyde. In general the additives of the present invention also include a diluent compatible with the electroplating bath in which the additive is to be used. The most preferred diluent is water.

In general the amount of formaldehyde present in the condensate should not be large. Thus for example, a content of formaldehyde equivalent to a mole ratio 1 mole of formaldehyde to 10 moles of reaction product is adequate. Smaller amounts than this can also be used. The purpose of the condensation is to improve the stability of the reaction product for storage purposes. The amount of formaldehyde should not however, be such as to destroy the properties of the additive useful in the electrodeposition of tin. Preferably the ratio of formaldehyde to reaction products is 8:100 or less.

The invention also includes a method of producing an additive for an electroplating bath which comprises reacting a sulphonating agent with an aromatic hydroxy compound having either of the general formulae defined above at a temperature below 120 C. preferably below C. The mole ratio of sulphonating agent to aromatic hydroxy compound should not in general exceed 2:1 and is preferably 1.5 :1. Most preferably the ratio is 1:1 or at most 1.2: l.

The preferred sulphonating agent is a mixture of sulphuric acid and acetic anhydride and is used primarily for temperatures below 80 C. Other sulphonating agents may be used however. Thus, for example sulphuric acid itself or chlorosulphonic acid may also be used, as also may be fuming sulphuric acid, but in this case the amount of free S0 should not be such as to cause degradation of the reaction product. In general amounts up to 20% of free S0 may be used, but amounts in excess of 20% free 80;, begin to cause degredation, the amount of de gradation increasing sharply. At 60% S0 almost complete degradation of the product occurs. A mixture of sulphuric and acetic acids may also be used provided the temperature is held below C.

The temperature of the reaction should of course be held below that at which decomposition of the reaction product occurs. In most cases temperatures below C. should be used. Preferably the temperature is below 100 C. and most preferably below 80 C. Reaction should not in general be allowed to proceed for longer than one hour at higher temperatures though longer periods may be used at lower temperatures (e.g. below 80 C.). The effect of higher temperatures is to produce larger quantities of tarry products which can give rise to difliculties in the electroplating bath. Whilst such tarry products can be removed by solvent extraction of the reaction product with an aromatic solvent such as monochlorbenzene it has been found that better separation of tars is achieved if the reaction product is formed in the presence of such a solvent for the tars. Such solvents when present during the reaction must be inert to the reactants and reaction product and must be substantially incompatible with water. The amount of tarry products formed is lower at lower temperatures although the actual quantity of reaction product at lower temperatures is also lower, i.e. the yield of reaction product is lower at lower temperatures.

At the end of the reaction of the sulphonating agent with the aromatic hydroxy compound the reaction mixture is diluted with water and any precipitated material filtered off at this stage. If a solvent for the tars was not present during the reaction solvent extraction may be performed on the filtrate to remove or reduce the amount of any tars which still remain therein.

If the condensation of the reaction product with formaldehyde is desired then this reaction should be carried out after dilution with water. A 30% solution of formaldehyde in water for example may be used and the condensation reaction carried out at an elevated temperature, e.g. 80 to 100 C. The duration of the condensation reaction may be for example from minutes to 60' minutes, but preferably should not exceed 30 minutes. Other substances such as paraformaldehyde which releases formaldehyde under the conditions of the reaction may be used in place of formaldehyde. The condensation with formaldehyde may be carried out either before or after filtration. If carried out before filtration then a certain proportion of the formaldehyde will react with the unreacted aromatic hydroxy compounds and will not find its way into the reaction product. In general the amount of formaldehyde should not be more than 1 mole formaldehyde for every 10 moles of aromatic hydroxy compounds originally present in the reaction mixture. Smaller quantities are in general usually desirable.

The degree of dilution with water of the reaction product may be for example from to 100 parts by volume of water per 100 parts of undiluted reaction product. The act of dilution causes a proportion of the undiluted aromatic polyhydroxy compound to precipitate, the proportion precipitated increasing with the degree of dilution. The filtered solution can itself be used as an additive to an electroplating bath. Alternatively, as indicated above, solvent extraction can be practiced on such a filtered solution, and/or the condensation with formaldehyde can be performed. In general the additives of the invention are added to electroplating paths for the electroplating of tin to an equivalent of about 1 /z4 gms. of reaction product or condensate per litre.

The invention will be further illustrated by reference to the following examples:

EXAMPLE 1 228 gms. diphenylol propane and 100 gms. sulphuric acid 98% were heated to 80 C. and stirred for 1 hour. The mixture was then cooled to below 40 C. and diluted with 100 gms. water. The solution was again cooled and left for several hours for undesirable solids to crystallise, and then filtered to remove the insoluble matter. The solution was then ready to be used in an electroplating bath.

EXAMPLE 2 228 gms. diphenylol propane and 100 gms. sulphuric acid 98% were heated to 80 C. and stirred for 1 hour. The mixture was then cooled to below 40 C. and 100 gms. water added and the diluted solution heated to 70 C. 8 gms. formaldehyde in the form of a solution in water was added and the mixture heated to 95 C. for 15 minutes. The solution was then cooled and was ready for use in an electroplating bath.

EXAMPLE 3 228 gms. diphenylol propane and 100 gms. sulphuric acid 98% were heated to 80 C. and stirred for 1 hour. The mixture was then cooled to below C. 100 gms. water were added and the diluted mixture again cooled and left for several hours after which insoluble matter was filtered off. The filtrate was heated to 70 C. and 8 gms. formaldehyde in the form of a 30% solution in water were added followed by further heating to 95 C. for 15 minutes. The mixture was then cooled after which it was ready for use.

A comparison of the additive and modified additive of the invention with the conventional dihydroxydiphenyl sulphone is illustrated below in Example 4.

4 EXAMPLE 4 An electroplating bath was prepared from 50 gms./litre stannous sulphate and 70 gms./ litre phenol sulphonic acid, 60% solution. The electrolyte was filtered before use.

The following Hull Cell tests illustrate the effectiveness of the prepared additives.

250 ccs. of the filtered electrolyte was placed into a Hull Cell of 300 ccs. capacity. The temperature of the bath was maintained at 60 C. and a 3 amps current supply for 1 minute was used.

The following table illustrates the usable range of current density obtained with the diluted additives of Examples 1, 2 and 3 at three levels of addition compared with dihydroxy diphenyl sulphone, when used in the electrolyte prepared as previously described.

Amperes per square foot;

2 gms./litre 1 4 gms./litre l 6 gms./litre l Dlhydroxydiphenyl sulphone- 175-273 140252 130-252 Example L. 60-231 70-273 60-315 Example 2.- 60-252 60-273 60-273 Example 3 60273 60-273 60-252 1 Gms. of solution.

EXAMPLE 5 5 gms. of di-ortho-hydroxy phenyl (methane) of the formula:

OH OH GEO and 2.5 gms. of 98% sulphuric acid were heated for 1 hour at C. The reaction mixture was then diluted with 3.8 ccs. of cold water and quickly cooled. The product was a clear dark red solution dissolving in the electroplating bath without noticeable formation of tar. The.

effective range of current density obtained was to 217 (using 0.5 gm. at a temperature of 60 C.).

EXAMPLE 6 5 gms. of di-para-hydroxy phenyl methane of the formula:

5 gms. of ortho-hydroxy-phenyl-para-hydroxy-phenyl methane of the formula:

and 2.5 gms. of 98% sulphuric acid were heated for 1 hour at 80 C. The reaction mixture was then diluted with 3.8 ccs. of cold water and quickly cooled. The reaction product was identical in appearance and behaviour to that in Example 6. The current density obtained was from to under the same conditions.

EXAMPLE 8 2.28 gms. of di(4-hydroxy-5-methyl) methane of the formula:

and 1 gm. of 98% sulphuric acid were heated together for 1 hour at 80 C. The reaction mixture was then diluted with 1.6 ccs. of water and quickly cooled. The resulting product was deep red in colour and gave a plating range of 80 to 185 (0.5 gm. at 60 C.).

EXAMPLE 9 0.43 gm. of di(4-hydroxy 6-methyl-phenyl) methane of the formula:

CH3 CH and 0.2 gm. of 98% sulphuric acid were heated for 1 hour at 80 C. The reaction mixture was then diluted with 0.3 cc. of water and quickly cooled. The product again was deep red in colour and gave plating range of 80 to 252 (0.5 gm. at 60 C.)

EXAMPLE 10 0.43 gm. of di(para-hydroxy-phenyl)-methyl methane of the formula:

H -Q- -Q- and 0.2 gm. of sulphuric acid were heated for 1 hour at 80 C. The reaction mixture was then diluted with 0.3 cc. of water and quickly cooled. The resulting product was a clear red coloured liquid which gave some yellow coloured deposit in the electroplating bath. The plating range was found to be 90 to 252 (2.5 gms. at 50 C).

When the same compound was reacted with chlorsulphonic acid instead of sulphuric acid under identical conditions the finished product had the appearance and behaviour of the corresponding product using sulphuric acid, except that the plating range was slightly extended to the range of 90 to 294 (0.5 gm. at 60 EXAMPLE 11 5.14 gms. of di-(4-hydroxy-5-methyl)-dimethylmethane of the formula:

EXAMPLE 12 12.1 gms. of di-(para-hydroxy-phenyl) methyl-ethylmethane of the formula:

and 5 gms. of sulphuric acid were heated together at C. for 1 hour. The reaction mixture was then diluted with 9 ccs. of water and cooled. The resulting product was dark red in colour and produced a little tar and a quantity of solid precipitate in the plating bath. The current density range Was 80 to 230 (0.5 gm. at 60 C.).

EXAMPLE 13 22.8 gms. of diphenylol propane and 10 gms. of sulphuric acid (98%) were reacted at room temperature. The sulphuric acid was added to the diphenylol propane, which addition caused the temperature to rise to approximately 40 C., but this temperature was quickly reduced to room temperature by cooling. The mixture was stirred for 12 hours and then diluted with 16.4 ccs. of water. After standing for several hours the mixture was filtered and 10 to 12 gms. of solid matter was removed. The clear liquid filtrate which remained gave good quality plating and a wide current density range of 80 to 301 (0.5 gm. at 60 0.).

EXAMPLE 14 45.6 gms. of diphenylol propane and 23.3 gms. of chlorsulphonic acid were reacted at room temperature, the reaction mixture being stirred for 12 hours and then diluted with 35 ccs. of Water. After standing for several hours, the precipitated solids were removed by filtration, 15 to 18 gms. of dry solid being removed by this means. The remaining filtrate gave good quality plating and a wide range of current density 80 to 294 (0.5 gm. at 60 C.).

EXAMPLE 15 22.8 gms. of diphenylol propane and 9.2 gms. of fuming sulphuric acid (20% S0 were reacted at room temperature, the acid being added slowly with cooling. The temperature tended to rise during the addition, reaching 40 to 45 C. at times. After the addition of acid was complete the reaction was cooled to room temperature and kept there for 6 hours. The mixture was then diluted with 16 ccs. of water and after cooling and standing for several hours, the solid material was removed by filtration. The amount of solid material separated was 8 to 10 gms, leaving a clear filtrate which gave good quality plating and a range of 80 to 301 in respect of current density (0.5 gm. at 60 C.).

EXAMPLE 16 22.8 gms. of diphenylol propane were reacted with 11.7 gms. of chlorsulphonic acid, reaction being conducted at 80 C. for 40 minutes with stirring. The reaction mixture was then diluted with 17 ccs. of water and cooled. Approximately 2 to 3 gms. of solid material were removed by filtration, leaving a clear liquid filtrate which gave a good plating effect with a current density range of 70 to 252 (0.5 gm. at 60 C.).

EXAMPLE 17 22.8 gms. of diphenylol propane were reacted with 9.2 gms. of fuming sulphuric acid at 80 C. for 40 minutes with stirring. The reaction mixture was then diluted with 16 ccs. of water, cooled and filtered to remove 1.5 to 2 gms. of solid, leaving a clear liquid filtrate. The filtrate gave good quality plating and a current density range of 70 to 252 (0.5 gm. at 60 (3.).

EXAMPLE 18 22.8 gms. of diphenylol propane were reacted with a mixture of 10 gms. of sulphuric acid and 10.2 gms. of acetic anhydride. The sulphuric acid and acetic anhydride were carefully mixed together whilst keeping the temperature below 40 C. The mixture thus obtained was then added to the diphenylol propane and the mass stirred for 1 hour at 80 C. The reaction mixture was then diluted with 20 ccs. of water and cooled. No separation of solid took place and the clear liquid could be used without fil- 7 tration. The plating properties were found to be good with a current density range of 60 to 252 (0.5 gm. at 60 C.).

EXAMPLE 19 100 parts of acetic anhydride were added to 100 parts of sulphuric acid with stirring and cooling the temperature of the mixture being kept below 40 C. To this mixture were added 140 parts of monochlorobenzene followed by 228 parts of diphenylol propane. The mass was stirred for two hours at 60 C. and then diluted with 200 parts of water, stirred, cooled and then allowed to separate into an upper monochorbenzene layer containing tarry biproducts and a lower aqueous layer containing the reaction product. The aqueous layer was separated from the monochlorobenzene layer and the small quantity of solvent still remaining therein removed by distillation under vacuum.

The resulting additive when added to a plating bath for tin gave a good plating with current density range of 70 through 252 (0.5 gm. at 60 C.).

EXAMPLE 20 The procedure of Example 19 was repeated but using dichlorobenzene instead of monochlorobenzene. This substitution results in the aqueous layer being the upper instead of the lower layer as in Example 19. The resulting reaction product had the same plating properties as that of Example 19, namely good plating with a current density range of 70-252 (0.5 gm. at 60 C.).

I claim:

1. In an aqueous acidic tin electroplating bath composition the improvement which comprises having present the reaction product of a sulfonating agent and at least one aromatic hydroxy compound having the general formula:

R2 R R wherein:

R and R are each selected from the group consisting of hydrogen and alkyl group having from 1 through 4 carbon atoms,

R and R are each selected from the group consisting of hydrogen, alkyl groups having from 1 through 4 carbon atoms and the hydroxyl radical, and one of the R radicals and one of the R radicals is a hydroxyl radical,

R is hydrogen when one of the R radicals is an alkyl radical and is selected from the group consisting of hydrogen and alkyl groups having from 1 through 4 carbon atoms when one of the R radicals is hydro- R is hydrogen when one of the R radicals is an alkyl radical and is selected from the group consisting of hydrogen and alkyl groups having from 1 through 4 carbon atoms when one of the R radicals is hydrogen,

wherein the mole ratio of sulfonating agent to said aromatic hydroxy compound is not greater than 1.5 to 1.

2. A composition as set forth in claim 1 in which the sulfonating agent is a mixture of sulfuric acid and acetic anhydride.

3. A composition as set forth in claim 1 in which the aromatic hydroxy compound is di-(p-hydroxyphenyl)-dimethyl methane.

4. In an aqueous acidic tin electroplating bath composition the improvement which comprises having present the condensation product of formaldehyde with the reaction product as defined in claim 1.

5. A composition as set forth in claim 4 wherein the mole ratio of formaldehyde to reaction product in the condensation product is up to 1 to 10.

6. In the electroplating of tin on iron or steel, the improvement which comprises adding to an aqueous acidictin electroplating bath, a reaction product of a sulofnating agent and at least one aromatic hydroxy compound having the general formula:

wherein R and R are each selected from the group consisting of hydrogen and alkyl groups having from 1 through 4 carbon atoms,

R and R are each selected from the group consisting of hydrogen, alkyl groups having from 1 through 4 carbon atoms and the hydroxyl radical, and one of the R radicals and one of the R radicals is a hydroxyl radical,

R is hydrogen when one of the R radicals is an alkyl radical and is selected from the group consisting of hydrogen and alkyl groups having from 1 through 4 carbon atoms when one of the R radicals is hydrogen,

R is hydrogen when one of the R radicals is an alkyl radical and is selected from the group consisting of hydrogen and alkyl groups having from 1 through 4 carbon atoms when one of the R radicals is hydrogen,

wherein the mole ratio of sulfonating agent to said aro matic hydroxy compound is not greater than 1.5 to 1.

References Cited UNITED STATES PATENTS 1,237,405 8/ 1917 Stiasny 260-49 1,443,697 1/ 1923 Croad 260-49 1,801,461 4/1931 Somerville 260--5 12 1,987,749 1/1935 Pine 20454 2,029,387 2/ 1936 Pine 204-54 X r 2,177,420 10/1939 Noerr et al. 26049 2,205,949 6/ 1940 Schwartz 260-5 12 2,370,986 3/ 1945 Nachtman 204-54 OTHER REFERENCES Chen Syntans and Newer Methods of Tanning (1950), pages 27-36 and 51, publ. by Chemical Elements, S. Lancaster, Mass.

DANIEL E. WYMAN, Primary Examiner.

W. H. CANNON, Assistant Examiner US. Cl. XQR. 260-5 12 

